Oxygen monitors

Richard Pitman asks about the necessity of monitoring oxygen levels in the
presence of liquid nitrogen gas. I don't know what the law says in your
region, but after a near fatality experienced at one of our facilities, we
have made it an internal policy that no one goes near a liquid nitrogen
storage tanks or freezers without wearing one of those small personal oxygen
monitors, even when working out in the open.
They are nifty battery operated gadgets, about the size of your average
pager, and you can either clip it onto your belt or carry it in your coat
pocket while working. They broadcast a very audible bleep the moment the
oxygen level drops below +/- 18%, giving you ample time to clear the area.
They shouldn't be to expensive in your neck of the woods, and it should be
noted that they must be returned to the agents for service and
re-calibration once a year.
Mike Kirby.
S.A.I.M.R
Johannesburg
South Africa.